Preparation of chromic salts



1953 A. STOVER 2,650,239

L 3 PREPARATION OF canouxc sun-s Filed April 18, 1952 Mire/2 0v PEACWON MACH/2E Z l'l z INVENTGR. lV/LL/AM ,4. 5701/52 Patented Aug. 25, 1953 raEraRArIoN or crmoMIc SALTS William A. Stover,fPitman, N. J assignor to S! cony-Vacuum .Oil Company corporation of New York Incorporated, a

Application April 18, 1952, Serial No. 282,978

7 claim (01. 260-438) This application is a continuation-in-part of my copending applicationserial No. 174,594, filed July 18,1950, and issued as U. 8. Patent No. 2,615,031 on October 21, 1952. ,There is described and claimed in the latter application a process for preparing a chromic salt of a low molecular weight fatty acid, such aschromicacetate, by reducing a hexavalent chromium compound with glycolic acid in the presence of alow molecular weight fatty acid. i The present invention relates specificallyto an improvement in such process. More particularly, the instant invention is concerned with; an improved procedure for the production of chromic acetate.

It has been discovered, in accordance with the process described herein, that the efficiency of reduction of hexavalent chromium to trivalent chromium using a reducing agentof glycolic acid in the presence of a low molecular weightfatty acid is greatly improved when the reaction is carried out in the substantial absenceof water. The absence of appreciable water in the aforesaid reactionresults in the directproduction. of the chromic salt of the low molecular weight fatty acid present, giving rise to a product of improved quality. a i l Unreduced (Irin the product is decreased to a negligible amount. While the description which follows hereinafter is directed particularly to the preparation of chromic acetate by reaction of glycolic acid, a dichromate, and acetic acid as the fatty acid, the instant method may likewise be employed with advantage in the production ofthe chromic salts of other low molecular weight fatty acids, the upper-limitof molecular weight being defined by a mono-basic fatty acid having not over'6 carbon atoms.

The chromium reactant employed inthe instant process is a water-soluble compound containing chromium of valence 6. Representative compounds include chromium 'trioxide, the 1 water-soluble metal chromates and the watersoluble metal dichromates. The latter group of compounds and, in particular, the alkali metal dichromates are preferred for use inthe present process. Particular preference is accorded sodium dichromate and potassium dichromate.

The procedure of the present process comprises contacting a chromium compound of the above type with a low molecular weight fatty acid in the substantial absence of water, i. e. under conditions such that the initial reaction mixture contains less than about 10 percent 'by weight of water, heating this mixture to a temperature of at least 120 F. and thereafter slowly adding glycolic: acid. After the addition ofgly colic acid, the resultingmixture is digested at an elevated temperature until evolution of carbon dioxide has ceased. Preferably the temperature to which the initial mixture of chromium compound and fatty acid is heated should lie within the range'of -230" F. although with the use of pressure, higher temperatures may be employed. Glycolic acid is preferably added to the hot initial mixture slowly and gradually over a period generally not exceeding about 8 hours. Thereafter, the mixture is maintained at a temperature of about to about 230 F. until evolution of carbon dioxide ceases.

Having described in a general Way the nature of this invention, the following specific examples will serve to illustrate the process described above:

Example 1 298 grams of sodium dichromate and 360 grams of glacial acetic acid were mixed and heated at atmospheric pressure in an autoclave equipped with an efficient reflux condenser and a mixer. After heating to a temperature of 120 F... 153 grams of glycolic acid in the form of a 71.6% by weight aqueous solution were slowly added over a period of approximately 1 hour, during which time the temperature was allowed to rise to the refiux temperature of 225-230" F. The amount of water in the reaction mixture was 5.3 per cent by weight. Following the addition of glycolic acid, the temperature was maintained at 225-230 F. for 1 hour, at which time evolution of carbon dioxide from the reaction mixture had ceased. Upon completion of the reaction, the mixture analyzed as follows: a

The calculated acetate/Cr+ mol ratio of the above solution was 3 to 1. Theextremely small amount of Cr+ in the resulting product indicates that substantially complete reduction of sodium dichromate to chromic acetate was accomplished.

The following examples were carried out by the procedure of Example 1, that is, by adding glycolic acid to a boiling solution of sodium dichromate and acetic acid. Reflux was continued as in Example 1 until evolution of carbon dioxide ceased. In these examples, however,the water content of thereactants was altered by the use of aqueous solutions of acetic acid in place of the glacial acid used in Example 1 1 Free Acidin Product Water 111 Unreduced E l XE d geagtion P a in xamp e Pmetlt 1x ure, Percent roducty Percent Mols HA Percent From the above table, it will be seen that both the quality of the product as indicated by the free acid-and the efiiciency of reduction as indicated by the presence of unreduced Cr+ 1n the product are impaired by the presence of an appreciable amount of water. H of the above data presented graphically in the attached drawing wherein the per cent weight of unreduced Cr+ in the product-is plotted against the per cent weight of water in the reaction mixture, it will be noted that the amount of unreduced Cr+ is practically nil when the amount of water in the reaction mixture isless than about 10 per cent. It is further to be noted that when the amount of water in the reaction: mixture risesabove. about 10. .per cent by j weight, the quantity or unreduced Cr theproductgreatly. increases. It is accordingly preferred; in accordance with the. instant processto effect the reduction or dichromatewith glycolic acid int-he presence of a, low molecular weight fatty acid'and in the presence oi not more than about 19- per cent by weight oiwater. Asin the processdescribed in my copending zapplicationserial NO; 174594, now U. St, 2,615,031, it is preferred in the present method to ghave an acetate/Cr+ ratio of at least about 2.5. With the use of such a ratio, reduction of dichromate with'glycolic acid in' the presenceof acetic acid under'reflux and'in the substantial absence of water providedbetter than 99% re- :duction and. produceda "more stable chromic acetate than was-produced when the reaction was effected in the presence of an appreciable amount of water of greater than about 10' per cent by weight. Different ratios-of-gl'ycolic acid to dichromate may be used to'aecomp-l'ish reduction of the die-hromate but it has" been found that the most efficient reduction is obtained when about 1.4 moles of glycolicacid are reacted with 1 mole of diohromate in the presenceofacetic acid.

Am-{added advantage achieved by carrying out the reaction described herein in the substantial absence ofwateris that the minimum temperaturewh-ichmay be employed is appreciably lower than that wherein the reaction is carried out in an excessive amount of water. The use of a lower operatingtemperature, as will be apparent, is a distinct advantage from a commercial'standpoi'nt.

Fromthe examples set forth herein, it will be noted that glycolic' acid in the presence of afatty acid, such as: acetic acid,,- and. in the presence of notmore than. about 10 percent by weight oi water 'providesan efi'ective reducing medium for conversion of a. chromium compound in which chromium has a valence of 6 tothe fatty acidchrom-ic salt, When such reaction is carried out in the substantial ab,- sence of water, the efliciency of reaction and the quality of the resulting product are distinctly improved as: compared with the. corresponding reductioncarried out, in the.- presence i an excessive amount of water.,

It; is to be-understood that the above description is merely illustrative of, preferredembodiments of the invention, of which many varia- From the results tions may be made within the scope of the following claims by those skilled in: the art without departing from the spirit. thereof.

1 claim;

1. A process for preparing the chromic salt of a low molecular weight fatty acid, which comprises reducing Cr+ to Cr, a reaction mixture containing not'more than about 10 per cent by weight of water, with glycolic acid in the presence of a, monobasic fatty acid having not more than 6 carbon atoms.

2.. Av process for preparing chromic acetate, which comprises reduction of Cr+ to Cr+ with glycolicacid in the presence of acetic acid and not-more'than about 10 percent by weight of water.

3. A process for preparing a chromic salt of a low molecular weight fatty acid, which comprises reducing a dich-romate, in a reaction mixture containing not-morethan about 10- per cent by weight of water, with glycolic acid'in the presence of a monobasic fatty acid having not more than 6 carbonatoms. g

4. A process for-preparing chromic acetate, which comprises reducing-- a dichrom'ate, with glycolic acid inth-e presence of acetic-acid, and not more than about 10- per cent by weight of water.

5. A process ior'preparing a chromic salt of a low molecularwei'ght fatty acid; comprises contacting, in areactionmixture containing not more than aboutifi per c'entby weight of water, a metal dichromate and cement:- basic fatty acidihavinginotmore than c. carbon atoms, heating the resulting mixture tea temperature. of at least .E., adding. glycolicxacid to the heated. reaction; mixture: and, after" completing the addition of .glycolic-cacid digesting the mixture at elevated temperature until evolution of carbon dioxide therefrom. has

ceased. o 7 o c 6. A. pnrocess: for preparing chromic acetate, which comprises: contacting, in a:v reactionv mix: ture: containing not more; than about 10 per cent by weight of water, a metal; dichromate and acetic acid, heating the resulting mixture to a. temperature of at least 129 F., adding glycolicgacidto the heatedmixtureand, aftercomplating the addition, or;- glycolic, acid, digesting the mixture at an; elevated temperature: until evolution of carbon dioxide therein-tom has ceased. V V

7'. A process tor. preparing chromic acetate, which comprises contacting, ina reaction/mixturecontainmg' not mor e =than about. 1:6 per cent by weight.-oi., water,,an alkali, metal diehromate-and glacial acetic acid, heating'the resulting mixture to a. temperature of at least 1-20 F.+.g-radua1lyadding :to-the heated mixture abeutlsiv moles otglycolic acid for each-mole of alkali metalchromatecontained therein and thereafter-digesting the mixture at refluxtemperature until evolution or", carbon dioxide therefromceasesi Av sTovnn...

References Cited in the 'file 'p'fthi'Si patent ,UNITED STATES PA ENTS 

1. A PROCESS FOR PREPARING THE CHROMIC SALT OF A LOW MOLECULAR WEIGHT FATTY ACID, WHICH COMPRISES REDUCING CR+6 TO CR+3, IN A REACTION MIXTURE CONTAINING NOT MORE THAN ABOUT 10 PER CENT BY WEIGHT OF WATER, WITH GLYCOLIC ACID IN THE PRESENCE OF A MONOBASIC FATTY ACID HAVING NOT MORE THAN 6 CARBON ATOMS. 